The present invention relates to a method for the production of solid solutions of sparingly soluble pesticides, pulverulent products that are obtained by said method and use thereof for pesticide formulations.
Pesticides that are sparingly soluble in aqueous media present difficulties during formulation, because with active substances of this kind it is not easy to develop formulations in which the pesticide is bioavailable. One approach is to form solid solutions, in which the pesticide is incorporated in molecularly disperse form, often with the result that much higher bioavailability is achieved.
The term solid solution is often used incorrectly in the literature, as materials with embedded solid crystalline substances are often called solid solutions. Strictly speaking, these are solid dispersions. In this text, solid solution means a true molecularly disperse distribution.
To date, the production of these solid solutions has been a very expensive process.
The following methods are currently available:    1. Melting of active substance and polymer at high temperature and extrusion (see for example WO 03/028453). This method has the disadvantage that high temperatures act on the active substance for some minutes and in addition large molded bodies are formed, requiring laborious comminution by grinding, to be made suitable for granulation or tableting. Furthermore, during melt extrusion, in addition to thermal loading there is also the action of shearing forces, which can lead to decomposition of the active substances.    2. Dissolution of active substance and polymer in an organic solvent, which dissolves both, and evaporation of the solvent or spray drying, alternatively dissolution of the active substance in an organic, water-miscible solvent and dissolution of the polymer in water (see for example WO 05/046328). This method has in itself the disadvantage that it requires extensive use of organic solvents, which are harmful to the environment and pose an explosion hazard, and appreciable costs are incurred when they are used.    3. Dispersion of active substance in an aqueous polymer solution, for example by wet grinding and spray drying. In this case, if the active substance is not water-soluble, solid solutions are not formed, only solid dispersions, which certainly do not have the same properties as molecularly disperse solutions, particularly with respect to bioavailability.